Land surface temperature is how hot the “surface” of the Earth would feel to the touch in a particular location. From a satellite’s point of view, the “surface” is whatever it sees when it looks through the atmosphere to the ground. It could be snow and ice, the grass on a lawn, the roof of a building, or the treetops in a forest. Thus, land surface temperature is not the same as the air temperature that is included in the daily weather report.

An anomaly is when the conditions depart from average conditions for a particular place at a given time of year. The maps show daytime land surface temperature anomalies for a given month compared to the average conditions during that period between 2000-2008. Places that were warmer than average are red, places that were near normal are white, and places that were cooler than average are blue. The observations were collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite.

Some land surface temperature anomalies are simply random weather phenomena, not part of a specific pattern or trend. Others anomalies are more meaningful. Widespread cold anomalies may be an indication of a harsh winter with lots of snow on the ground. Small, patchy warm anomalies that appear in forests or other natural ecosystems may indicate deforestation or insect damage. Many urban areas also show up as hot spots in these maps because developed areas are often hotter in the daytime than surrounding natural ecosystems or farmland. Warm anomalies that persist over large parts of the globe for many years can be signs of global warming.